Fix #248: Class cannot inherit from refinement types

We now check that classes do not inherit from refinement types
(unless they are an encoding of parameterized types), nor from
& or | types.

3 files changed, 20 insertions, 14 deletions

diff --git a/src/dotty/tools/dotc/core/Types.scala b/src/dotty/tools/dotc/core/Types.scala
index 017b7cadc..987014ff4 100644
--- a/src/dotty/tools/dotc/core/Types.scala
+++ b/src/dotty/tools/dotc/core/Types.scala
@@ -700,15 +700,20 @@ object Types {
 
     /** If this is a (possibly aliased, annotated, and/or parameterized) reference to
      *  a class, the class type ref, otherwise NoType.
+     *  @param  refinementOK   If `true` we also skip non-parameter refinements.
      */
-    def underlyingClassRef(implicit ctx: Context): Type = dealias match {
+    def underlyingClassRef(refinementOK: Boolean)(implicit ctx: Context): Type = dealias match {
       case tp: TypeRef =>
         if (tp.symbol.isClass) tp
-        else if (tp.symbol.isAliasType) tp.underlying.underlyingClassRef
+        else if (tp.symbol.isAliasType) tp.underlying.underlyingClassRef(refinementOK)
         else NoType
-      case tp: TypeVar => tp.underlying.underlyingClassRef
-      case tp: AnnotatedType => tp.underlying.underlyingClassRef
-      case tp: RefinedType => tp.underlying.underlyingClassRef
+      case tp: AnnotatedType => tp.underlying.underlyingClassRef(refinementOK)
+      case tp: RefinedType =>
+        if (refinementOK) tp.underlying.underlyingClassRef(refinementOK)
+        else {
+          val tycon = tp.withoutArgs(tp.argInfos)
+          if (tycon eq tp) NoType else tycon.underlyingClassRef(refinementOK)
+        }
       case _ => NoType
     }
 
diff --git a/src/dotty/tools/dotc/typer/Checking.scala b/src/dotty/tools/dotc/typer/Checking.scala
index 17cba1373..9e13ec13b 100644
--- a/src/dotty/tools/dotc/typer/Checking.scala
+++ b/src/dotty/tools/dotc/typer/Checking.scala
@@ -248,7 +248,7 @@ trait Checking {
    *  @return  `tp` itself if it is a class or trait ref, ObjectClass.typeRef if not.
    */
   def checkClassTypeWithStablePrefix(tp: Type, pos: Position, traitReq: Boolean)(implicit ctx: Context): Type =
-    tp.underlyingClassRef match {
+    tp.underlyingClassRef(refinementOK = false) match {
       case tref: TypeRef =>
         if (ctx.phase <= ctx.refchecksPhase) checkStable(tref.prefix, pos)
         if (traitReq && !(tref.symbol is Trait)) ctx.error(d"$tref is not a trait", pos)
diff --git a/src/dotty/tools/dotc/typer/Inferencing.scala b/src/dotty/tools/dotc/typer/Inferencing.scala
index 9e34d549a..05be46f29 100644
--- a/src/dotty/tools/dotc/typer/Inferencing.scala
+++ b/src/dotty/tools/dotc/typer/Inferencing.scala
@@ -106,14 +106,15 @@ trait Inferencing { this: Checking =>
    *  class type reference where the class has a companion module, a reference to
    *  that companion module. Otherwise NoType
    */
-  def companionRef(tp: Type)(implicit ctx: Context): Type = tp.underlyingClassRef match {
-    case tp: TypeRef =>
-      val companion = tp.classSymbol.companionModule
-      if (companion.exists)
-        companion.valRef.asSeenFrom(tp.prefix, companion.symbol.owner)
-      else NoType
-    case _ => NoType
-  }
+  def companionRef(tp: Type)(implicit ctx: Context): Type =
+    tp.underlyingClassRef(refinementOK = true) match {
+      case tp: TypeRef =>
+        val companion = tp.classSymbol.companionModule
+        if (companion.exists)
+          companion.valRef.asSeenFrom(tp.prefix, companion.symbol.owner)
+        else NoType
+      case _ => NoType
+    }
 
   /** Ensure that the first type in a list of parent types Ps points to a non-trait class.
    *  If that's not already the case, add one. The added class type CT is determined as follows.